texture-rectangle: update _new_with_size in line with master

This updates the cogl_texture_rectangle_new_with_size() api in line with
master to be consistent with other texture constructors. This removes
the internal_format and error arguments and allows the texture to be
allocated lazily which means the texture can be configured with apis
like cogl_texture_set_components() and cogl_texture_set_premultiplied()
before it is allocated.

Reviewed-by: Neil Roberts <neil@linux.intel.com>